An ultrathin sheet of semiconductor is like the film of a soap bubble, but made of tungsten and selenium atoms. If you poke it with a sharp diamond needle, tiny defects appear at that spot. At low temperatures, these defects start to glow, but not in a continuous stream, rather strictly one photon at a time.
The researchers tested 76% of the pokes: in almost every spot, a bright point-like light source appeared. It didn't flicker, didn't jitter in frequency, and when tested for single-photon emission, it indeed emitted exactly one photon, not a pair. Moreover, such a source can be turned on and off with an electric voltage, like a light bulb with a switch.
This method works on a standard glass-silicon substrate — the same kind already used for photonic microchips. This means single-photon sources could be integrated directly into quantum devices, where photons travel along waveguides like cars on highways.
A single photon is so little light that the human eye wouldn't see it even after a million years of continuous observation.
In the series 'The Expanse', quantum communication works thanks to single photons that cannot be intercepted unnoticed.